The present invention relates to arc welding and more particularly to an apparatus for applying nonreactive gas to weld surfaces having varying configurations.
Reactive metals (i.e., titanium, zirconium, and hafnium) at elevated temperatures have high solubilities for oxygen, nitrogen, and hydrogen. The dissolution of relatively small amounts of these gases into the metals significantly affects the metals' physical properties. For example, the dissolution of oxygen and nitrogen significantly increase hardness while the dissolution of hydrogen reduces toughness and increases notch sensitivity.
Oxygen, nitrogen, and hydrogen are all present in the atmosphere. Therefore, when welding reactive metals it is critical to scrupulously shield from the atmosphere that portion of the reactive metal which would be at elevated temperatures (i.e., molten weld pool, hot solidified weld metal, and adjacent heat-affected zone). The shielding is normally accomplished by surrounding the area to be protected by a nonreactive gas such as argon or helium.
The shielding of the molten weld pool is conventionally provided by a torch shield. The torch shield is disposed at the terminus of the welding torch and consists of a cup open at one end through which an electrode protrudes. This shield advances in the direction of the welding and therefore does not shield either the solidified weld metal or the adjacent heat-affected zone. In order to protect this area, a trailing shield is employed. The conventional trailing shield consists of a rigid housing which is mounted to the welding torch and configured to provide effective shielding to a predetermined surface configuration.
Various problems exist with rigidly constructed trailing shields. For example, if the surface configuration changes or another workpiece of different configuration is to be welded, the trailing shield would have to be replaced with one adapted to the particular surface configuration. Similarly, if no trailing shield is available for a particular surface configuration, less than adequate shielding will be provided.